Introduction
After a well has been drilled, it must be properly completed before it can be
put into production. A complex technology has evolved around the techniques
and equipment developed for this purpose. The selection of such equipment
and techniques should only be made following a thorough investigation of the
factors which are specific to the reservoir, well and production system under
study.
put into production. A complex technology has evolved around the techniques
and equipment developed for this purpose. The selection of such equipment
and techniques should only be made following a thorough investigation of the
factors which are specific to the reservoir, well and production system under
study.
Three Basic Requirements
There are three basic requirements of any completion, in common with almost
every oil field product or service.
every oil field product or service.
A completion system must provide a means of oil or gas production (or injection) which is:
- Safe
- Efficient / Economic
- Reliable
Completion System Requirements
Current industry conditions may force operators to place undue emphasis on
the economic requirement of completions. However, a non-optimized system
may compromise long term company objectives. For example, if the company
objective is to maximize the recoverable reserves of a reservoir or field, a poor
or inappropriate completion design can seriously jeopardize achievement of
the objective as the reservoir becomes depleted.
In short, it is the technical efficiency of the entire completion system, viewed
alongside the specific company objectives, which ultimately determines the
completion configuration and equipment used.
the economic requirement of completions. However, a non-optimized system
may compromise long term company objectives. For example, if the company
objective is to maximize the recoverable reserves of a reservoir or field, a poor
or inappropriate completion design can seriously jeopardize achievement of
the objective as the reservoir becomes depleted.
In short, it is the technical efficiency of the entire completion system, viewed
alongside the specific company objectives, which ultimately determines the
completion configuration and equipment used.
Definition of Well Completion
Well completion involves a process which extends far beyond the installation
of wellbore tubulars and equipment. To highlight this fact, the following
definition of the term “completion” is presented:
conveying, pumping or controlling production or injection fluids.
of wellbore tubulars and equipment. To highlight this fact, the following
definition of the term “completion” is presented:
- Completion: The design, selection and installation of tubulars,
conveying, pumping or controlling production or injection fluids.
Under this definition, installing and cementing the production casing or liner,
as well as logging, perforating and testing, are part of the completion process.
In addition, complex wellhead equipment and processing or storage
requirements affect the production of a well and so may have some bearing on
the design and configuration of the completion.
History and Evolution of Oil and Gas Well Completions
As the understanding of reservoir and production performance has evolved,
then so too has the systems and techniques put in place as part of the completion
process.
Early wells were drilled in very shallow reservoirs which were sufficiently
consolidated to prevent caving. As deeper wells were drilled, the problems
associated with surface water prompted the use of a casing or conductor to
isolate water and prevent caving of the wellbore walls. Further development
of this process led to fully cased wellbores in which the interval of interest is
perforated.
Modern completions are now commonly undertaken in deep, hot and difficult
conditions. In all cases, achieving the completion and eventual production
objectives are a result of careful planning and preparation.
then so too has the systems and techniques put in place as part of the completion
process.
Early wells were drilled in very shallow reservoirs which were sufficiently
consolidated to prevent caving. As deeper wells were drilled, the problems
associated with surface water prompted the use of a casing or conductor to
isolate water and prevent caving of the wellbore walls. Further development
of this process led to fully cased wellbores in which the interval of interest is
perforated.
Modern completions are now commonly undertaken in deep, hot and difficult
conditions. In all cases, achieving the completion and eventual production
objectives are a result of careful planning and preparation.
Completion Types
There are several ways of classifying or categorizing completion types. The
most common criteria for the classification of completions include the
following:
most common criteria for the classification of completions include the
following:
- Wellbore/reservoir interface, i.e., open-hole or cased hole, horizontal completion
- Producing zones, i.e., single zone or multiple zone production
- Production method, i.e., natural flowing or artifically induced production (Artificial Lift)
Open Hole or Barefoot Completions
Barefoot completions are only feasible in reservoirs with sufficient formation
strength to prevent caving or sloughing. In such completions there are no
means of selectively producing or isolating intervals within the reservoir or
open hole section. The production casing or liner is set and cemented in the
reservoir cap rock, leaving the wellbore through to the reservoir open.
The use of open hole completions is now restricted primarily to some types of
horizontal wells and to wells where formation damage from (air drilling) drilling
fluids is severe. To prevent an unstable formation from collapsing and plugging
the wellbore, slotted screen or perforated liners may be placed across the open
hole sections.
strength to prevent caving or sloughing. In such completions there are no
means of selectively producing or isolating intervals within the reservoir or
open hole section. The production casing or liner is set and cemented in the
reservoir cap rock, leaving the wellbore through to the reservoir open.
The use of open hole completions is now restricted primarily to some types of
horizontal wells and to wells where formation damage from (air drilling) drilling
fluids is severe. To prevent an unstable formation from collapsing and plugging
the wellbore, slotted screen or perforated liners may be placed across the open
hole sections.
Example of Openhole Completions
Perforated Completions
The evolution and development of efficient and reliable perforating tools and
logging services has enabled complex completions to be designed with a high
degree of efficiency and confidence. Modern perforating charges and
techniques are designed to provide a clear perforation tunnel through the
damaged zone surrounding the wellbore. This provides access to the undamaged
formation, allowing the reservoir to be produced to its full capability.
Cased and cemented wells generally require less complex pressure control
procedures during the early stages of installing the completion components.
Efficient reservoir interpretation and appraisal techniques combined with a
high degree of depth control, enables selective perforating. This helps ensure
the successful completion and production of modern-day oil and gas wells by
precisely defining which zones of the reservoir will be opened for flow.
Multiple zone completions are often used in reservoirs with complex structures
and production characteristics. The ability to select and control the production
(or injection) of individual zones is often the key to ensuring the most efficient
production regime for the field or reservoir. Consequently, modern multiple
completions may be complex but maintain a high degree of flexibility and
control of production.
logging services has enabled complex completions to be designed with a high
degree of efficiency and confidence. Modern perforating charges and
techniques are designed to provide a clear perforation tunnel through the
damaged zone surrounding the wellbore. This provides access to the undamaged
formation, allowing the reservoir to be produced to its full capability.
Cased and cemented wells generally require less complex pressure control
procedures during the early stages of installing the completion components.
Efficient reservoir interpretation and appraisal techniques combined with a
high degree of depth control, enables selective perforating. This helps ensure
the successful completion and production of modern-day oil and gas wells by
precisely defining which zones of the reservoir will be opened for flow.
Multiple zone completions are often used in reservoirs with complex structures
and production characteristics. The ability to select and control the production
(or injection) of individual zones is often the key to ensuring the most efficient
production regime for the field or reservoir. Consequently, modern multiple
completions may be complex but maintain a high degree of flexibility and
control of production.
Examples of Cased Hole Completions
continued